Reaction centres of ionic and quasi-ionic polymerizations: a concerted study

J.Kříž (e-mail: kriz@imc.cas.cz)

Coworkers: J.Dybal, P.Schmidt, B.Masař, R.Puffr, J.Stehlíček(+),B.Masař,P.Vlček, L.Lochmann, M.Janata

Monomers: N-acyllactams, lactams, acrylates and methacrylates

Polymerizations: cationic, activated anionic, quasi-anionic, GTP

Methods:

preparation and reactions of model compounds and living oligomers
NMR: ¹H,²H,⁶Li,⁷Li,¹³C,¹⁹F,²³Na,²⁹Si,³¹P,⁷⁵As,¹²¹Sb 1D and 2D spectra, relaxations in laboratory and rotating frame, quadrupolar effects, multiple quantum NMR
FT-IR and Raman spectra
MO LCAO calculations: MNDO, ab initio SCF up to 6-31_**G and DFT

General overview: The structure and dynamics of growth centres determine the polymerization mechanism. In the case of ionic or quasi-ionic polymerizations, few direct information on them had been at hand untill recently. The present study is centered in the Department of Spectroscopy but carried out in collaboration with other departments of the Institute of Macromolecular Chemistry. It is based on a concerted system of experimental and theoretical methods of investigation. Given the limitation of any of these methods, only those results which simultaneously agree with spectroscopic observations, chemical experience and theoretical calculations are considered to be reliable.

Cationic polymerization of N-acyllactams: Polymerizations initiated by Ph₃CMeX₆ ( Me=As,Sb) or SnX₄ (X=F,Cl) have been shown^1-3 to proceed on carbenium ion growth centres with the coupled counterion MeX₆^- or SnX₅^- partly coordinated to the penultimate carbonyl group even in strongly solvating media such as DMSO. The result for SnX₄ indicates its auto-ionization to SnX₃⁺SnX₅^- as the first initiation step.

Activated anionic polymerization of lactams: The activated monomers (or lactam salts) with the Li, Na, K or MgX counterions have been shown⁴to form mostly ion pairs and, under usual polymerization concentrations, their higher aggregates. However, the rate of exchange between aggregates and simple pairs is several orders of magnitude larger than the propagation rate so that it does not complicate the polymerization kinetics. The activated monomer forms a loose complex with the N-acyllactam growth centre⁵in which both the incoming and terminal lactam molecules appear to be equivalent and weakly bonded to the central nitrogen atom.

Anionic or quasi-anionic polymeriyation of (meth)acrylates: Low-molecular 2-lithioesters such as 2-lithio methyl or tert-butyl isobutyrate form dimeric, trimeric and tetrameric aggregates even in THF and at low concentrations^6,7. Chemical exchange between them proceeds with a rate which could interfere with anionic polymerization. The type of Li bonding depends on the aggergation or coordination degree but is in all cases only partly covalent. The structure of the 2-lithioester group is a compromise between a 2-lithioester and an ester-enolate. Aggregation as well as coordination supports its enolate nature. The typical aggregate has a core of 4 Li and 4 O atoms arranged in a roughly cubical geometry and held together with a cooperative system of electron-defficient covalent bonds and coulombic interaction^7-12. In living oligomers starting with the dimer, lithium is additionally coordinated to the penultimate ester group^11,12. This coordinated structure is in dynamic equilibrium with the open or uncoordinated one in solvating media such as THF but much less so in non-polar solvents such as toluene. By detailed quantum chemical calculation, this difference can be shown¹³ to be the reason of the different stereoregularity of growth.

¹J.Kříž,R.Puffr, NMR study of the structure of poly(N-benzoyl-8-octanelactam), J.Polym.Sci.,B: Polymer Phys. 31,789(1993)

²J.Kříž,R.Puffr, NMR study of the propagation centre in cationic polymerization of N-benzoyl-8- octanelactam.I.The structure of model living oligomers,J.Polym.Sci.,B: Polymer Phys. 31,1705 (1993)

³J.Kříž,R.Puffr, NMR study of the propagation centre in cationic polymerization of N-benzoyl-8- octanelactam. II. Investigation of the propagation center,J.Polym.Sci.,B: Polymer Phys. 32,1129 (1993)

⁴J.Kříž,J.Stehlíček,J.Dybal,J.Hauer,P.Schmidt, Study of the propagation centre in the anionic polymerization of lactams, 1. Spectroscopic and theoretical study of the activated monomer in dimethyl sulfoxide, Macromol.Chem.Phys.197,467(1996)

⁵J.Kříž,J.Stehlíček,J.Dybal,J.Hauer,P.Schmidt, Study of the propagation centre in the anionic polymerization of lactams, 2. Model study of the interaction between the activated monomer and N-acylllactam in dimethyl sulfoxide, Macromol.Chem.Phys.197,483(1996)

⁶J.Kříž,J.Dybal,P.Vlček,M.Janata, Spectroscopic study of methyl 2-lithioisobutyrate, Macromol. Chem.Phys. 195,3039 (1994)

⁷J.Dybal,J.Kříž, MNDO and ab initio calculations of methyl 2-lithioisobutyrate and its solvates and aggregates, Collect.Czech.Chem.Commun. 59,1699 (1994)

⁸J.Kříž,J.Dybal,M.Janata,P.Vlček, NMR and MNDO study of the complexes of methyl 2-lithioisobutyrate and of the living methyl methacrylate oligomer with lithium tert-butoxide, Magn. Reson.in Chem. 32, S8 (1994)

⁹J.Kříž,J.Dybal,M.Janata,P.Vlček, NMR and quantum chemical study of the initiation systems containing tert-butoxide or lithium 3-methylpentan-3-olate, Macromol. Chem. Phys. 196, 3117 (1995)

¹⁰J.Kříž,J.Dybal,L.Lochmann,M.Janata,P.Vlček, NMR study of the model dimer in THF, Macromol. Chem.Phys. 196,3005 (1995)

¹¹J.Dybal,J.Kříž, MO LCAO SCF study of the model dimer, its solvation and aggregation states, Collect.Czech.Chem.Commun. 60,1609 (1995)

¹²J.Kříž,J.Dybal,M.Janata,L.Lochmann,P.Vlček, Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers. 7.Interaction of the model living dimer with lithium tert-butoxide in THF, Macromol.Chem.Phys.,197,1889(1996)

¹³J.Dybal,J.Kříž, Study of the propagation centre in the anionic ...,8.ab initio SCF, AM1 and MNDO study of the mechanism of MMA addition to the anionic growth centre, Macromol. Simulations, 6, 437-450 (1997)

¹⁴C.Zune, P.Dubois, R.Jérôme, J.Kříž, J.Dybal, L.Lochmann, M.Janata, P.Vlček, T.M.Werkhoven, J.Lugtenburg: Study of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR and MO LCAO study of the interaction of di-tert-butyl 2-lithio 2,4,4'-trimethylglutarate and the living poly(tert-butyl methacrylate) oligomers with lithium 2-(2-methoxyethoxy)ethoxide in tetrahydrofuran. Macromolecules 31: 2731-2743 (1998).

¹⁵C.Zune, P.Dubois, R.Jérôme, J.Kříž, J.Dybal, L.Lochmann, M.Janata, P.Vlček, T.M.Werkhoven, J.Lugtenburg: Study of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR and MNDO study of the complexes of di-tert-butyl 2-lithio-2,4,4'-trimethylglutarate and of the living poly(tert-butyl methacrylate) oligomers with lithium chloride. Macromolecules 31: 2744-2755 (1998)

¹⁶C.Zune, P.Dubois, R.Jérôme, J.Grandjean, J.Kříž, J.Dybal, L.Lochmann, M.Janata, P.Vlček: Study of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR study of di-tert-butyl 2-lithio-2,4,4'-trimethylglutarate and living poly(tert-butyl methacrylate) oligomers in THF/toluene. Macromolecules, in print